General System Description
General System Description
The DI and DI/APC Systems are described in the following.
The DI system is fitted in the Saab 9000 M88. There are two versions of the DI/APC system:
- for Saab 9000 M89-M90
- for Saab 9000 M91-M93.
Saab DI system M88
The Saab 9000 M88 is equipped with the Saab DI (Direct Ignition) ignition system. The DI system also affects the cabling for the APC system but has a separate control module.
Ignition system
The DI/APC is a combined ignition and boost pressure control system. It was introduced in model year 1989 on Saab 9000 cars equipped with the B202L engine.
The ignition system is of capacitive type and consists of 4 ignition coils and electronic circuitry built into the ignition discharge module. The ignition coils are controlled by electronic circuitry in the ignition discharge module which is in turn controlled via low-level outputs from the control module.
On starting, the ignition system produces sparks on two spark plugs simultaneously, 1 and 4 or 2 and 3, for a number of successive proper combustion processes. On the basis of the ionization currents flowing through the spark plugs and information from the crankshaft position sensor on the position of the crankshaft, the system then has sufficiently accurate information to synchronize the sparks with the right cylinder.
To improve starting performance at low engine speeds, the ignition system generates a "multispark" (10° BTDC - 20° ATDC).
The crankshaft position sensor consists of a Hall sensor and a field rotor. The Hall sensor is mounted behind the crankshaft pulley. The field rotor has three gaps and is mounted on the inside of the crankshaft pulley.
Ignition timing
Ignition timing is calculated by the control module chiefly on the basis of the following information:
- engine load (load signal from LH)
- engine speed
- knocking, if any
- throttle position (only when idling, from LH)
Knock control
The DI/APC system incorporates a knock sensor of piezoelectric type. In the event of knocking, the system slightly retards the ignition. If the knocking persists, the ignition will be retarded even more and boost pressure will also be reduced.
M91 and later modifications
A number of modifications have been introduced on M91 and subsequent versions of the DI/APC system.
The system has more extensive diagnostics facilities using the ISAT scan tool, with more diagnostic trouble codes and a larger number of command codes as compared with earlier versions.
A new DI/APC control module has been developed together with a new temperature sensor fitted ahead of the throttle body.
The manifold absolute pressure (MAP) sensor is discontinued as a separate component. The pressure sensor function is provided instead by the load signal from the LH system together with the intake air temperature signal.
A number of other new functions have also been added:
- torque limitation in low gears (engine variants with automatic transmission)
- spark plug burn-off when the engine is switched oft (irrespective of ignition switch position)
- fuel enrichment on knocking (LH 2.4.2 Turbo)
- engine rpm dependent ignition timing at idling speed.